Rubella, a mild, contagious illness characterized by an erythematous maculopapular rash, is observed primarily in children 5–14 years of age and in young adults. The disease, commonly called German or 3-day measles, may be with no symptoms or may involve a 1- to 5-day prodromal period of malaise, headache, cold symptoms, low-grade fever, and suboccipital lymphadenopathy.
Although the illness is mild in children, it may cause the congenital rubella syndrome in the fetus of a mother infected early in pregnancy. As many as 85% of infants infected during the first 8 weeks of gestation have detectable defects by 4 years of age. The classic abnormalities associated with the rubella syndrome include congenital heart disease, cataracts, and neurosensory deafness. After 20–24 weeks of gestation, congenital abnormalities are rare.
The quantitative measurement of IgG antibodies to rubella virus aids in the determination of immune status. Assay results of 10 IU/mL of antibody are negative or not immune. Assay results above 10 IU/mL are considered positive or immune. A positive result of IgM antibody indicates a congenital or recent infection. The measurement of IgM class antibodies for determination of acute-phase infection is recommended in all age groups. IgM rubella antibody determination is usually not recommended when the patient is older than 6 months. Unlike IgG class antibodies, IgM antibodies are larger molecules and cannot cross the placenta, thus determining that the infant has an active form of the disease.
Negative for rubella IgG antibodies by ELISA or chemiluminescence (<7 IU/mL: no immunity)
Negative for IgM antibodies by ELISA or chemiluminescence (<0.9 IU/mL: no infection)
Positive for rubella IgG antibodies by ELISA or chemiluminescence (>10 IU/mL; immunity, indicates a current or previous exposure or immunization to rubella)
Positive for rubella IgM antibodies (with or without positive IgG) by ELISA or chemiluminescence (>1.1 IU/mL; indicates a current or recent infection with rubella virus)
Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions. Label the specimen with the patient’s name, date, and test(s) ordered and place in a biohazard bag for transport to the laboratory.
Follow-up testing may be required.
When testing for IgG antibody, seroconversion between acute and convalescent sera is considered strong evidence of a current or recent infection. The recommended interval between an acute and convalescent sample is 10–14 days.
A serum specimen taken very early during the acute stage of infection may contain levels of IgG antibody below 10 IU/mL.
Although the presence of IgM antibody suggests current or recent infection, low levels of IgM may occasionally persist for more than 12 months after infection or immunization. Passively acquired rubella antibody levels (IgG) in the infant (which can cross the placenta because of their smaller molecular size) decrease markedly within 2–3 months after infection.
IgM is detectable soon after clinical symptoms occur and reaches peak levels at 10 days.
Pretest Patient Care
Assess patient’s test knowledge. Explain test purpose and procedure. Advise pregnant women that rubella infection acquired in the first trimester of pregnancy is associated with an increased incidence of miscarriage, stillbirth, and congenital abnormalities.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment. Advise women of childbearing age who test negative to be immunized before becoming pregnant. Immunization is contraindicated during pregnancy. Patients who test positive are naturally immune to further rubella infections.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.